Take many hundreds of job losses, add the fact they're in a strategic industry, stir in the end of more than half a millennium of shipbuilding history and top it all up with the raw politics of Scottish independence. What you have got is a very potent brew.

Two key questions are likely to dominate the political reaction to the news that shipbuilding is to end at Portsmouth:

1. Have English shipyard workers paid the price for keeping jobs in Glasgow?

First things first: why are the job losses happening at all?

Cuts were always inevitable after the completion of two massive aircraft carriers - a once in 30 or 40 year event.

Even the placing of orders for 13 new frigates was never going to replace the lost work.

What's more, cuts to the defence budget mean that there's a gap between the end of work on the carriers and the start of work on Type 26 Global Combat Ships.

Government and industry insiders insist that the choice of Govan over Portsmouth was a decision first considered over three years ago - long before Alex Salmond was even re-elected as First Minister of Scotland in 2011 let alone the announcement of a referendum date.

It was discussed as part of the Strategic Defence and Security Review carried out as soon as the coalition came to power in 2010.

A senior defence industry figure has told my BBC colleague John Moylan that BAE Systems recommended to government that shipbuilding at Portsmouth should end as long as two years ago.

He said: "This is not about Scotland and independence - closing shipbuilding at Portsmouth is the sensible strategic decision for the long term."

I'm told that Govan has two advantages over Portsmouth - a lower cost base and a partnership with the Scotstoun shipyard on the other side of the Clyde.

Tory strategists point out that it's hardly in their political interests to save a Scottish shipyard and part close an English one.

Nevertheless, it's clear that there can be no decision on something as significant as the building of warships without a great deal of political calculation.

As I reported yesterday, one well-placed source told me that the government was "acutely conscious of the politics of the Clyde" and did not want to give Alex Salmond a gift a little less than a year ahead of the independence referendum.

2. If Scotland votes next year to become an independent nation will "rump UK" (or whatever what is left will be called) have to depend on a foreign country to build its warships?

Not necessarily.

Shipbuilding will not end immediately at Portsmouth. Even when it does some of those employed in the city by BAE Systems will continue working on ship repair and maintenance.

Work on the new frigates will begin long after the Scottish referendum vote.

It will be interesting to examine the deal the government does with BAE to see whether it includes a "get out" clause allowing work on the frigates to be transferred from Glasgow to Portsmouth if Scotland votes for independence.

Govan's local Labour MP Ian Davidson wants just such a clause as part of his campaign to persuade people to vote No in the referendum.

One of those who has been consulted about this decision told me that if Scotland votes No it would still be possible to switch work to England.